The invention concerns a mechanism for tensioning and positioning reel cores, especially in machines for winding and unwinding webs of paper and cardboard, with a cylindrical tensioning component that is mounted on a journal rigidly connected to a driveshaft or brake shaft, that expands radially when its circumference moves relative to the journal, and that interlocks with the core by way of elevations distributed around its outside circumference.
Many mechanisms for tensioning and positioning reel cores with a tensioning component mounted on a journal that is concentrically connected to a driveshaft or brake shaft and that expands radially when its circumference moves relative to the journal in order to tension the core are known. A generic mechanism is described for example in European C 0 208 832.
When heavy reels of paper are wound or unwound, the known tensioning mechanisms are very effective for positioning and securing the reels against the cores as long as the torque that occurs when the reel is braked or accelerated and that is to be transmitted increases with the weight of the reel. When on the other hand torque is to be avoided in a heavy reel (e.g. three metric tons), the known tensioning mechanisms have considerable drawbacks.
Since they cannot position the reel precisely until they have expanded, torque must be applied to attain the expansion, leading to a relative motion between the tensioning head and the reel, increasing the wear on the reel, and contaminating the measurement of speed of rotation by way of the journal. Furthermore, a tensioning head that employs spreading structures often exhibits out-of-control motion and load processes between the supporting journal and the structures that undergo the spreading, leading to severe enough wear to destroy the tensioning heads relatively early. Sealing out dust represents another problem in that the moving parts need to be lubricated.